Screw-cutting lathes



tates Pate it O 2,865,241 SCREW-CUTTING LATHES Benjamin J. Farrow, Wimborne, Dorset, England Claims priority, application Great Britain January 15, 1954 2 Claims. (Cl. 82--23) This application is a division of my application Serial No. 415,129, now Patent 2,756,623.

This invention relates to means for efiecting disengagement of the traversing carriage of a screw-cutting lathe from the lead screw at the end of a cut.

According to the invention the apparatus comprises a half-nut device for engaging the lead screw, a member carrying the half nut device and mounted on the carriage apron, resilient means for continually urging the half nut device in the direction of disengagement, hand operable means, a lost motion connection between the hand operable means and the member such that movement of either of said means and member also impart movement to the other except for some lost motion, locking means for effecting a positive locking of said half nut device in said position, and an unlocking device actuated by said operating means for device to its unlocking position at the beginning of the disengagement movement while the lost motion is being taken up and abutment means connected to said hand operable means and engageable with a stop at the end of the required cut whereby said abutment means is moved thereby first unlocking the locking means while taking up the lost motion and thereafter moving the member to the fully disengaged position should the spring fail to do so.

By means of the invention a positive engagement is effected and the parts locked in position during cutting, but instantaneous disengagement is eflectcd automatically to terminate the cut whereby screw cutting can be effected at high speeds as well as low speeds without risk of spoiling the work or the tool by continuing the out too far along the work. Disengagement can also be effected at any time by hand.

A constructional form of the invention will now be described by way of example in greater detail with reference to the accompanying diagrammatic drawings wherein:

Figure 1 is a rear view of a lead screw and an apron with apparatus attached thereto made in accordance with the invention;

Figure 2 is a similar view but showing the parts in a ditierent position;

Figure 3 is a front view thereof;

Figure 4 is a sectional view on ure 1; and

Figure 5 is an end view looking in the direction of the arrow in Figure 3.

The apron is to be attached to the carriage of a lathe in the usual manner, and has a half-nut 11 to be engaged with a lead screw 12 for traversing the carriage and tool thereon along the work for cutting the thread. The apron carries the usual traversing handle 13 geared by pinion 14 to a rack on the side of the lathe bed.

The half-nut 11 is mounted by a bolt 16 on a lever 17 that is pivoted at 18 on the apron at some distance from the half-nut. The lever is urged by a spring 19 the line 44 on Figpushing the locking carrying the half-nut in its disengagement direction and is provided with a slot 20 engaged by a pin 21 for moving it positively into engagement. The pin 21 is carried by a lever 23 that is mounted on a spindle and boss 24 mounted pivotally in the apron. A hole may be provided instead of the slot 20. The pin 21 has some play in the slot or hole to provide a lost motion effect. The pin and slot or hole are arranged in such position that movements of either of the levers 17, 25 in either direction will move the other of theselevers in the same (engagement or disengagement) direction. connected to the boss.

A locking pawl 27 is pivoted to the apron at 28and is urged by a spring 29 to bring the nose of the pawl overthe end of the lever 17 to lock the parts in the position of engagement as shown in Figure 1. The lever 23 carries a pin 30 which pushes the pawl off the lever 17 during the disengagement movement.

The apron is provided with a boss 32 in which is mounted a spindle 33 that carries a pinion 34 on its inner end that engages the lead screw, and carries an abutment plate 35 on its outer end which has one or more slots 36 in its periphery disposed in positions corresponding to recurring positions on the lead screw.

39 in the apron and can ride on the periphery of the plate 35.

In operation, commencing with the parts in the positions of disengagement shown in Figure 2, the operator presses the arm 25 upwards so that the pin 21 presses the lever 17 down until the pin 38 engages in the slot 36 or engages the periphery of the plate 35. If the pin engages in the slot all the parts move to the engagement position of Figure 1 as the slot will be in a position corresponding to the correct lead screw position for starting a cut. If the slot 36 is not so positioned the pin 38 will ride on the periphery of the abutment plate 35 until the correct starting position is reached whereupon the pin 38 will enter the slot and engagement will be effected.

At the position where the cut is to be terminated, the end of the lever 23 will engage a stop collar 40 on and adjustable along the lead screw whereby the lever 23 is turned downwards as the carriage advances. This causes the pin 30 to push the pawl 27 off the lever 17 and the latter is then immediately drawn up by the spring 19 to disengage the half-nut from the lead screw. While the pin 30 is pushing the pawl 27 off the lever 17 the pin 21 is taking up the lost motion in the slot 20. for any reason the spring 19 fails to pull the half nut out of engagement the pin 21 will immediately efiect pos itive movement of theparts to the disengaged positions, this being a very important safeguard.

The stop 40 could be mounted on the bed or other part of the lathe.

The half nut can also be disengaged at any time by the operator by moving the lever 25.

By means of the present invention disengagement can be effected with precision at the same position along the work irrespective of speed of the lead screw or the load imposed on the tool by varying depths of cut.

Iclaim:

1. Apparatus for use with a screw cutting lathe for releasing the carriage from the lead screw comprising a half-nut device for engaging the lead screw, a member device and mounted pivotally on the carriage apron on one axis, the half-nut device being spaced from said axis, resilient means for continually urging the half-nut device in the direction of disengagement, hand operable means mounted pivotally on the apron on another axis, a lost motion connection between Patented Dec. 23, 1958 An engagement arm 25 is The lever 17 carries a pin 38 that passes through a slot the hand. operable means and. the member such that movement of either of said hand operable means. and member also imparts movement to the other except for some lost motion, said resilient means acting on the hand operable means only through said. lost motion connection, locking means mounted on the apron movably for effecting a positive locking of said half-nut device insaid.

position, and an unlocking device, actuated by said hand operable meansforv pushing the locking device to its un-- locking position at the beginning of the disengagement movement while the lost motion is being taken up, a

stop, and abutment means fixed to said hand operable.

leasing the carriage from the lead screw comprising an apron, a half-nut device for engaging the lead screw, a lever member mounted pivotally on the apron on one axis and-carrying the half-nut device at some distance from its pivot, resilient means for continually urging the lever member and half-nut device in the direction of disengagement, a hand operable engagement lever pivotally mounted on the apron, on another axis, a pin carried by the engagement lever and projecting into a slot in the; lever member, said slot providing a lost motion gagement lever and. lever member also imparts move ment to the other except for some lost motion, a locking lever pivotally mounted on the apron on a third axis, spring means urging said. lockinglever towards its locking position, a projection on the locking lever engageable with said lever member to effect a. positive locking of said half-nut device in said position, a projection carried by said engagement lever and engageable with said locking lever to move the latter to its unlocking position at the beginning of the disengagement movement of the engagement lever while the lost motion is being taken up, and abutment means connected to said engagement lever and engageable with a stop at the end of the required cut wqereby said abutment means is moved thereby moving the means for unlocking the locking lever while taking up the lost motion and thereafter movingthe lever memher through the lost motion connection to the fully disengaged position should the springfailto do so;

References Cited in the file of this patent UNITED STATES PATENTS 2,101,754 Randall Dec. 7, 1937 2,399,045 Kylin Apr. 23, 1946 2,488,696 Waldron June 7, 1946 2,756,623 Farrow July 31, 1956 FOREIGN PATENTS 412,294 Germany Apr. 18, 1925 

